In rack-and-pinion type steering apparatuses, rack shaft that changes the turning angle of wheels via a tie rod is supported on the housing of the steering gear assembly in such a way as to be able to move back and forth, and a pinion shaft that transmits the rotation of the steering wheel to the rack shaft is rotatably supported on the housing by a bearing.
In such rack-and-pinion type steering apparatus, the pinion shaft may move in the radial direction or in the thrust direction due to a load exerted on the pinion shaft upon steering operation, whereby abnormal noise is generated or the steering force is varied. In view of this, the bearing with which the pinion shaft is rotatably supported is fixed to the housing thereby fixing the pinion shaft with respect to the radial direction and the thrust direction to prevent the generation of abnormal noise and the variation in the steering force.
Fixing the bearing by a ring nut is preferred in increasing the rigidity of the bearing with respect to the radial direction and the thrust direction. However, this leads to the problem of increase in the size of the steering gear assembly, because a space for accommodating the ring nut is needed.
Preloading the bearing with a tapered snap ring serving as a fastening ring leads to low cost and light weight and allows reduction in the size of the steering gear assembly because the space for accommodating the tapered snap ring may be small. However, fixing the bearing by a tapered snap ring leads to low rigidity of the bearing with respect to the radial direction and the thrust direction.
Consequently, a load exerted on the pinion shaft upon steering will press the tapered snap ring up in the axial direction or tilt it, whereby the pinion shaft will shift in the thrust direction to create a gap between the outer ring of the bearing and the housing. Then, the position of engagement of the pinion and the rack is displaced from the correct position, causing abnormal noise like slapping noise.
In a rack-and-pinion type steering apparatus disclosed in Japanese Patent Application Laid-Open No. 2010-038254, a plurality of conical projections are provided on a slanted surface of the tapered snap ring at regular intervals. In addition, an annular recessed groove is provided on the slanted surface of an annular groove, which is provided on the inner circumferential surface of the housing and in which the tapered snap ring is fitted. Thus, when an external force acts on the tapered snap ring in the axial direction to reduce the diameter of the tapered snap ring by a predetermined amount, the projections on the tapered snap ring comes into engagement with the inner wall of the annular recessed groove. This prevents the diameter of the tapered snap ring from decreasing more than the predetermined amount and restricts the displacement of the tapered snap ring in the axial direction. However, the rack-and-pinion type steering apparatus disclosed in Japanese Patent Application Laid-Open No. 2010-038254 is complex in the shapes of the tapered snap ring and the annular groove. This leads to the problems of difficult machining and increased manufacturing cost.